As mentioned in the first part of these studies [Notevarp & Weedon, 1936], the ratio between the two absorption bands of the antimony trichloride reaction for vitamin A is normally almost constant for potent preparations, but varies within wide limits for cod liver oils of usual potencies.Mittelmann [1925; 1927], in publications reviewed by Bezssonoff [1929], claimed to have prepared cod liver oils giving no blue colour until some oxidation had taken place. Hawk [1929] obtained some increase in the blue value on exposure of cod liver oils to air. Lovern et al. [1931] were not able to prepare oils giving no reaction, but found a considerable rise in the 603 m,u band on oxidation of very fresh oils. The 572 m, band remained approximately constant; this was confirmed by Heilbron et al. [1931]. We demonstrated earlier that very high concentrations of oil inhibited the 603 my band, but not the 572 m,u band, in fresh oils in which the 572 mp band predominated.
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